The present invention relates to a weighing apparatus, of the combinatorial weighing type, known as a computer scale.
A "computer scale" combinatorial weighing apparatus and its operation will briefly be described below.
The combinatorial weighing apparatus has a central distribution table of a conical configuration, a plurality of supply troughs disposed below a peripheral edge of the distribution table and arranged radially around the distribution table and a plurality of pool hoppers positioned respectively below radially outward ends of the supply troughs. Each of the pool hoppers has on its lower side a gate which is selectively openable and closeable. The combinatorial weighing apparatus also includes a plurality of weighing hoppers corresponding to numbers of pool hoppers. Each weighing hopper is associated with and positioned beneath a corresponding pool hopper. Each of the weighing hoppers also has on its lower side an openable and closable gate and is associated with a weight detector for weighing articles charged into the weighing hopper. A collection chute or receiving means is disposed below the weighing hoppers for collecting the articles discharged from the weighing hoppers and delivering them to a packaging unit.
In operation, articles to be weighed are transported by a supply unit such as a bucket conveyor to a position over the distribution table, and are dropped onto the latter around its tip or highest point. The distribution table is vertically reciprocably vibrated in helical motions by an electromagnetic vibratory unit to distribute the supplied articles substantially uniformly over the table in a radially outward direction toward the peripheral edge of the table. The distributed articles then fall off the peripheral edge of the distribution table into the supply troughs, which are reciprocably vibrated obliquely upwardly and downwardly by electromagnetic vibratory units disposed respectively below each of the supply troughs for delivering the articles radially outwardly to a distal end of each supply trough, from which the articles drop into the respective pool hoppers below. The vibratory motions of the distribution table and the supply troughs cause similar numbers of articles to be supplied into the pool hoppers in a unit period of time. When a number of articles close to a predetermined number are stored in each of the pool hoppers, upon elapse of a preset interval of time, the vibrations of the distribution table and the supply troughs are stopped, and the gates of selected pool hoppers are opened to allow the articles therein to be charged respectively into corresponding weighing hoppers positioned below the pool hoppers, in which the articles are weighed. The emptied pool hoppers are then supplied with articles through the foregoing article supplying operation until all of the pool hoppers are loaded again.
The weight values obtained by the weighing hoppers are computed by a computer in a combinatorial arithmetic operation to find a combination of weights which is equal or closest to a preset weight. The gates of the weighing hoppers that contain the articles which give such a combination of weights are opened to discharge the articles from the weighing hoppers into the collection chute. The discharge articles are gathered at a lower central portion of the collection chute, and then packed in a bag or the like. Articles are again charged into the emptied weighing hoppers from the corresponding pool hoppers, which become empty and will be supplied with articles again from corresponding supply troughs. Simultaneously, the foregoing weighing operation is repeated.
If the articles are supplied from the supply troughs directly to the weighing hoppers, disturbances in the flow rate of the articles in the supply troughs vary the intervals of time needed for the articles to be supplied to the weighing hoppers, and the time required for effecting the combinatorial weighing operatiou would increase, a time increase is a disadvantage because it decreases the number of weighing operations performed per minute. Therefore, pool hoppers are used in order to ensure that a desired number of weighing cycles are performed per minute.
The computer scale combinatorial weighing as described above is capable of delivering to a packaging step, a wide variety of articles in batches having a total weight equal or closest to a preset weight. Where the preset weight is quite small, such as 20 g for example, and thin, lightweight articles such as potato chips are supplied to the weight hoppers, say 10 in number, there is a tendency for the apparatus to perform the combinatorial weighing inaccurately or in extreme cases to fail to effect the combinatorial weighing. More specifically, articles being fed from the distribution table to the collection chute are supplied from the supply troughs to the respective pool hoppers by oblique vibratory movements of the supply troughs. The vibrations cause the articles to be advanced progressively in the supply troughs and then to fall into the pool hoppers. In order to select from all of the weighing hoppers uniformly throughout repeated weighing operations, it is required that the number of articles supplied to the weighing hoppers have a weight close to a preset weight value. To this end, the supply troughs are controlled in their vibratory motion on a time-dependent basis in order to supply an appropriate number of articles to each pool hopper.
When the weight of combined batches of articles is small and hence the articles fed to each pool hopper are lightweight, the vibratory supply by the supply troughs under the supply interval control is liable to allow the articles to drop en masse into the pool hoppers. This causes certain pool hoppers to be supplied with articles which give an excessive total weight. Where thin articles, such for example, potato chips, are to be weighed, those potato chips which are stuck together tend to be supplied without being separated and some pool hoppers may be overweighted. As a result, the combinatorial weighing operation based on weight values given by the weighing hoppers may suffer from a reduced combinatorial probability that the combined weights will be equal or closest to a preset weight, and sometimes the combinatorial weighing can not be performed.